The invention disclosed and claimed herein generally pertains to improved apparatus for illuminating film, containing a radiographic or other medical diagnostic image, for viewing and study. More particularly, the invention pertains to apparatus of such type which includes an improved light diffuser comprising layers or laminations of film material for increasing the amount of light transmitted therethrough.
View boxes are well-known types of devices used by radiologists to view and study radiographic images and other medical diagnostic images which are on film. Such images, showing selected views of body tissue, can be obtained by means of conventional X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and other techniques known to those of skill in the medical diagnostic imaging arts. By carefully studying such images, a radiologist can detect the presence of significant medical conditions in a patient or other subject, without the need for invasive surgery. Some important examples of such conditions include breast cancer, lung cancer, pneumonia, fracture, and arthritis.
A conventional view box generally is used to view medical diagnostic film which typically is on the order of 14 inches by 17 inches. Such a device contains one or more fluorescent tubes or other sources of light, and has a front panel typically comprising a translucent light diffuser, such as a sheet of milky white Plexiglas. Also, the dimensions of the front panel may be large enough to accommodate four films, placed side by side, at the same time. Each radiographic imaging film is placed on the light diffuser and transilluminated, for viewing and study, by light from the light source. The light passes through the diffuser and is diffused or scattered thereby. Thus, the light transmitted to the imaging film is of uniform brightness or intensity, so that the imaging film is uniformly illuminated. If a view box was not provided with a diffuser or other means for scattering light from the fluorescent tube light source, the fluorescent tubes would tend to be seen through the imaging film, interfering with the study thereof.
Radiographic films record an image as a pattern of silver crystals. Light from the view box can be either blocked or scattered by these crystals. This process produces a complimentary pattern in the light leaving the observer's side of the film. Some of this light travels to the observer's eye, and the pattern of light is focused onto his or her retina. In an ideal view box, the observed pattern of light would precisely correspond to the pattern of silver crystals in the film, accurately transmitting the film image to the observer.
The view box currently used in practice is not an ideal view box because it produces diffuse or scattered light, as stated above. Scattered light can randomly travel from one part of the film to another. More specifically, a scattered light ray may travel obliquely from a bright part of the imaging film into an adjacent dark part of the film, and then be scattered in the dark part of the film to the observer's eye. If this occurs, then the observer will perceive the scattered light ray as having come from the dark part of the film. The observer will then perceive the dark part of the film as being brighter than it actually is, which will decrease contrast between the bright and dark areas of the film. Most of this scatter occurs close to the border between the bright and dark areas of the film, thereby blurring the border and causing decreased resolution of the observed image. This can be thought of as a sort of leakage of light from the bright part of the film into the dark part of the film. Thus, the radiologist's task of correctly interpreting a film image is made more difficult. Certain conditions, such as breast cancer, lung nodules, and small pneumothorax (collapsed lung) are especially hard to detect in any event. If there is too much blurring of edges, or insufficient contrast between brighter and darker areas of a film image, a correct diagnosis of such conditions may not even be possible. The term "resolution," as used herein, means the level of sharpness which characterizes the boundary, or edge, between adjacent lighter and darker regions of an image.
In the past, it has been suggested that contrast of a medical diagnostic imaging film, illuminated by means of a view box, could be improved by substantially increasing the spatial separation between the light source and the imaging film. Thus, the light illuminating the film would become less diffuse. However, the proposed spatial separation was on the order of six to twelve feet, whereas the depth of a conventional view box is generally less than one foot. It would be highly impractical for a number of reasons, including cost and spatial constraints, to construct a view box having the proposed expanded dimensions.
U.S. patent application Ser. No. 08/610,218, filed Mar. 4, 1996 by William R. Brauer, the inventor herein, teaches the use of light directing film to collimate the scattered light projected toward radiographic imaging film, i.e., to substantially reduce the solid angle thereof. By illuminating the imaging film with collimated light rather than diffuse light, it has been found that contrast and resolution have been very significantly improved, when viewing the film. It was also found that collimation of scattered or diffuse light was particularly effective if multiple layers of the light directing film were employed. However, use of multiple light directing film layers tended to reduce the total amount of light passing therethrough to illuminate the imaging film. In order to ensure that sufficient light reached the imaging film, it was found necessary to increase the amount of light initially provided by the light source.
Moreover, as stated above, the flat front panel of a conventional view box may be made large enough to simultaneously accommodate four 14 inch by 17 inch diagnostic films placed in side-by-side relationship. This arrangement allows the radiologist to readily compare information provided by different films, such as films showing the same view of a patient at different times. Because of light diffusion in a conventional view box, the radiologist's field of view extends to the entire panel. Thus, he can view all four films at the same time, with comparatively little head or body movement. However, if collimated light is employed to illuminate imaging film on a view box panel, only light transmitted through a comparatively small region of the panel, and the film thereon, will be received by the radiologist's eye, while his eye is fixed at a specified position. Thus, use of collimated light can substantially diminish field of view. In a conventional view box, and particularly a view box for displaying multiple films, significant reduction in field of view could force a viewer to continually move his upper body, in order to view all the films on the front panel in their entirety. This, in turn, may cause fatigue and muscle stiffness, particularly if viewing of diagnostic film continues over a prolonged period of time.